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Jerome Guillen wants to gun a prototype Tesla Model S up a steep, twisty road on the outskirts of Silicon Valley, but a Porsche blocks his way.

Once Mr. Guillen, the Tesla Motors Ltd. manager in charge of readying the Model S for launch by July, gets some running room, he hits the electric car's accelerator. With only a soft rumble from the tires, the Tesla lunges up the steep curving road as effortlessly as any petroleum-fueled German machine.

The Tesla Model S and a Porsche 911 represent opposite poles of the automotive universe. The 911 is the peak of internal-combustion sports cars. The engine growls. The dashboard dials dance as the gears shift